JP5096933B2 - Antireflection film, optical component having the same, interchangeable lens, and imaging device - Google Patents

Description

  The present invention relates to an antireflection film in the visible range that is suitably used in an imaging apparatus such as an interchangeable lens for a single-lens reflex camera, an optical component having the same, an interchangeable lens, and an imaging apparatus.

  High-performance single-focus lenses and zoom lenses widely used in photographic cameras, broadcast cameras, and the like have a lens barrel configuration of a large number of lens groups. Generally, these lenses are composed of about 10 to 40 lenses. Some lenses, such as wide-angle lenses, target images with a wide angle of view, and the incident angle of light increases at the periphery of such wide-angle lenses. On the surface of these optical components such as lenses, a dielectric film having a refractive index different from the refractive index of the substrate is combined, and the thickness of each dielectric film is 1 / 2λ or 1 with respect to the center wavelength λ. Antireflection treatment by a multilayer film using an interference effect such as / 4λ is performed.

  The lens surface may be burned or scratched during the manufacturing process. In the burn phenomenon, when the optical glass is left in the atmosphere, a thin film is formed by elution of basic components in the glass due to condensation of water droplets on the glass surface or contact with water during the polishing process. There are a blue discoloration phenomenon and a white discoloration phenomenon in which components eluted from the glass cause some chemical reaction and precipitate as white spotted particles.

Japanese Laid-Open Patent Publication No. 5-85778 (Patent Document 1) discloses that an antireflection film is formed by laminating a plurality of dielectric films on the surface of a transmissive optical component substrate, and is closest to the substrate side of the antireflection film. An optical component having an antireflection film in which the composition of the first layer is silicon oxide (SiO _x , x: 1 ≦ x ≦ 2) and the film thickness nd is 0.25λ ₀ ≦ nd (λ ₀ is a design wavelength) Disclosure. According to such a configuration, even if burns or scratches are present on the surface of the optical component substrate, they can be made inconspicuous, but it is difficult to suppress the occurrence of burns.

  Further, a general antireflection film has a single layer or a layer structure of about two layers or three layers. When such an antireflection film is applied to the above-described lens barrel group, for example, when the reflectance of each antireflection film is 0.5% and the number of lenses in the lens barrel is 20, the number of lens surfaces is Since there are 40 surfaces, the transmittance is calculated to be 82%, resulting in a reflection loss of 18% on the way. In addition, multiple reflections occur in or between the lenses, resulting in a decrease in flare, ghost, and contrast that significantly degrade the target optical characteristics.

  In order to solve such problems, an antireflection treatment using an antireflection film having more layers has been performed. For example, Japanese Patent Application Laid-Open No. 10-20102 (Patent Document 2) discloses a seven-layer structure. Has disclosed an antireflective coating. Although this antireflection film has been improved to reflect about 0.3% of light with respect to light in the visible wavelength band, the antireflection performance is insufficient.

Japanese Unexamined Patent Publication No. 2001-100002 (Patent Document 3) discloses an antireflection film having a 10-layer structure made of MgF ₂ , SiO ₂ , Al ₂ O ₃ , and ZrO ₂ + TiO ₂ . This antireflection film has an antireflection characteristic with a reflectance of 0.1% for light in the visible wavelength band of 270 nm.

Japanese Unexamined Patent Publication No. 2002-107506 (Patent Document 4) discloses an antireflection film having a 10-layer structure made of MgF ₂ , SiO ₂ , Al ₂ O ₃ , and ZrO ₂ + TiO ₂ . This antireflection film has an antireflection characteristic with a reflectance of about 0.1% for light in the visible wavelength band of 300 nm.

  However, the antireflection film described in Patent Document 2 has a problem that the antireflection performance in visible light having a wavelength of around 400 nm or around 700 nm is insufficient. In addition, since the antireflection films described in Patent Documents 3 and 4 are antireflection films having a reflectance of about 0.1%, the transmittance becomes 96% in calculation when applied to the above-described number of lens barrel lenses of 20, and in the middle A reflection loss of 4% occurs and is not fully satisfactory.

  In JP-A-2005-352303 (Patent Document 5) and JP-A-2006-3562 (Patent Document 6), an antireflection film comprising a plurality of layers is formed on a substrate, and the substrate and the refraction of each layer are formed. The refractive index decreases in order from the base material, the refractive index difference between each adjacent layer and the substrate is 0.02 to 0.2, the physical layer thickness of each layer is 15 to 200 nm, and the outermost layer is a silica airgel layer A membrane is disclosed. However, antireflective properties are worse for high refractive index glass having a refractive index of 1.70 or more compared to low refractive index glass. In addition, since interchangeable lenses that require a high refractive index use glass materials that are easily burnt such as Lak, LaSF, LaF, and SF systems, there is a problem that burns and ghosts are likely to occur.

  JP-A-2007-94150 (Patent Document 7) defines the refractive index and optical film thickness of five or six layers, and has a reflectance of 0.05 with a 5 ° incident spectral reflection characteristic in a visible light wavelength region of 400 to 700 nm. An antireflection film capable of obtaining an antireflection effect of not more than% is disclosed. However, it does not have any effect as a countermeasure against burns on the substrate surface.

JP-A-5-85778 Japanese Patent Laid-Open No. 10-20102 Japanese Patent Laid-Open No. 2001-100002 JP 2002-107506 A JP 2005-352303 A JP 2006-3562 Japanese Unexamined Patent Publication No. 2007-94150

  An object of the present invention is to provide an antireflection film having excellent transmittance characteristics in a wide incident angle range, generating less flare and ghost, etc., and having an excellent anti-burning effect, and an optical component, an interchangeable lens, and the like An imaging device is provided.

  As a result of intensive studies in view of the above problems, the present inventors have found that the following antireflection film can provide excellent antireflection, flare and ghost prevention effects, and burn prevention effects in a wide incident angle range. The present invention has been conceived.

  That is, the antireflection film, optical component, interchangeable lens, and imaging device of the present invention have the following characteristics.

(1) An antireflection film in which a first layer and a second layer are laminated in this order from the substrate side on a substrate, and in the light of a wavelength region of 400 to 700 nm,
The refractive index of the substrate is 1.70 to 1.95,
The first layer is mainly composed of alumina, the optical film thickness is 98.5 to 133.5 nm, the refractive index is 1.59 to 1.68,
The second layer is a silica airgel layer, an optical film thickness of Ri 116.0 to 129.0 nm der antireflection film having a refractive index, characterized in that a 1.22 to 1.28.
( 2 ) In the antireflection film according to any one of the above (1) , the reflectance in the wavelength region 450 nm to 600 nm of 0 ° incident light is 0.5% or less, and the wavelength region of 30 ° incident light is 400 nm to 400 nm An antireflection film characterized by having a reflectance at 650 nm of 1.0% or less.
( 3 ) The antireflection film as described in (1) or (2) above, further comprising a fluororesin film having a thickness of 0.4 nm to 100 nm having water repellency or water / oil repellency on the second layer. An antireflection film characterized by that.
( 4 ) The antireflection film according to any one of (1) to ( 3 ), wherein the first layer is formed by a physical film formation method, and the second layer is formed by a wet method. Anti-reflective coating.
( 5 ) In the antireflection film according to any one of (1) to ( 4 ), the physical film-forming method is a vacuum deposition method, and the wet method is a sol-gel method. Prevention film.
( 6 ) An optical component comprising the antireflection film according to any one of (1) to ( 5 ) above.
( 7 ) An interchangeable lens comprising the optical component according to ( 6 ) above.
( 8 ) An imaging apparatus comprising the optical component according to ( 6 ).

  According to the present invention, an excellent antireflection effect can be obtained in a wide incident angle range in the visible light wavelength region of 400 to 700 nm by the two-layer antireflection film.

  In addition, the antireflection effect is extremely high in a wide incident angle range as compared with the conventional antireflection film, and it can be used for flare and ghost countermeasures and anti-burning of interchangeable lenses of single-lens reflex cameras used outdoors.

[1] anti-reflective coating
(1) Configuration of Antireflection Film An antireflection film 1 of the present invention formed on a substrate 3 is shown in FIG. The antireflection film 1 has a first layer and a second thin layer having a predetermined material or a predetermined refractive index and optical film thickness [refractive index (n) × physical film thickness (d)] on the surface of the substrate 3. Laminated.

For light in the wavelength region of 400 to 700 nm, the refractive index of the substrate 3 is 1.70 to 1.95, and the antireflection film 1 of the present invention is
A first layer 11 having an optical film thickness of 98.5 to 133.5 nm and mainly composed of alumina;
And an optical film thickness of 116.0 to 129.0 nm and a second layer 12 which is a porous layer mainly composed of silica.

  The refractive index of the first layer (alumina layer) 11 containing alumina as a main component is preferably 1.59 to 1.68, and more preferably 1.62 to 1.66. The optical film thickness of the alumina layer 11 is preferably 104.0 to 130.0 nm. Alumina has advantages such as high adhesion, high permeability in a wide wavelength band, high hardness, excellent wear resistance, and good cost performance. Alumina has excellent shielding properties against water vapor, and in particular, by using alumina as the main component of the first layer, it is possible to prevent burns on the substrate surface.

  The porous layer 12 mainly composed of silica of the second layer is preferably made of silica aerogel. Thereby, the layer which has a low refractive index is obtained, and the outstanding antireflection function can be exhibited. The refractive index of the second layer 12 is preferably from 1.22 to 1.28, more preferably from 1.23 to 1.27. The pore diameter of the porous layer is preferably 0.005 μm to 0.2 μm, and the porosity is preferably 20% to 60%. The optical film thickness of the second layer 12 is preferably 118.0 to 126.0 nm. The second layer 12 made of silica airgel may be subjected to a hydrophobic treatment. The hydrophobized silica airgel layer has excellent water resistance and durability.

(2) Material of the first layer The first layer 11 of the antireflection film of the present invention is mainly composed of alumina. The first layer 11 is preferably made of only alumina (aluminum oxide). The purity of alumina is preferably 99% or more.

(3) Second Layer Material The second layer is a porous layer 12 mainly composed of silica. Hereinafter, the generation of the material constituting the porous layer 12 will be described in detail.
(3-i) Preparation of organically modified silica dispersion
(3-i-1) Formation of Wet Gel A silica gel-forming compound and a catalyst are dissolved in a solvent, subjected to a hydrolysis polymerization reaction, and then aged to form a wet gel. A preferred specific formation procedure of the wet gel is shown below.

(a) Silica skeleton-forming compound
(a-1) Saturated alkoxysilane and silsesquioxane Silica sol and silica gel are produced by hydrolysis polymerization of alkoxysilane and / or silsesquioxane. The saturated alkoxysilane may be a monomer or an oligomer. The saturated alkoxysilane monomer preferably has 3 or more alkoxyl groups. By using a saturated alkoxysilane having three or more alkoxyl groups as a silica skeleton-forming raw material, an antireflection film having excellent uniformity can be obtained. Specific examples of saturated alkoxysilane monomers include methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, diethoxydimethoxysilane, dimethyldimethoxysilane, dimethyl Diethoxysilane is mentioned. As the saturated alkoxysilane oligomer, a polycondensation product of the above-mentioned monomers is preferable. Saturated alkoxysilane oligomers are obtained by hydrolysis polymerization of monomers.

Even when a saturated silsesquioxane is used as a raw material for forming a silica skeleton, an antireflection film having excellent uniformity can be obtained. Saturated silsesquioxane is a generic term for network-like polysiloxanes having a structural unit represented by the general formula RSiO _1.5 (where R represents an organic functional group). Examples of R include an alkyl group (which may be a straight chain or branched chain and having 1 to 6 carbon atoms), a phenyl group, and an alkoxy group (for example, a methoxy group, an ethoxy group, etc.). Silsesquioxane is known to have various structures such as a ladder type and a saddle type. Moreover, it has excellent weather resistance, transparency and hardness, and is suitable as a silica skeleton-forming raw material for silica airgel.

(a-2) Unsaturated alkoxysilane and silsesquioxane A monomer or oligomer of unsaturated alkoxysilane or silsesquioxane having an ultraviolet-polymerizable unsaturated group may be used as a silica skeleton-forming raw material. By using a material having an unsaturated group as a raw material for forming the silica skeleton, a silica airgel film having excellent toughness can be obtained even when the blending amount of the binder is small. The unsaturated alkoxysilane monomer has an organic group having at least one double bond or triple bond (hereinafter referred to as “unsaturated group”) and an alkoxyl group. The unsaturated group has 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms.

A preferred unsaturated alkoxysilane monomer is represented by the following general formula (1):
R ^a Si (OR ^b ) ₃ ... (1)
(Wherein R ^a represents an organic group having 2 to 10 carbon atoms having an unsaturated bond, and R ^b O represents an alkoxyl group having 1 to 4 carbon atoms).

The unsaturated group ^Ra is an organic group having at least one UV-polymerizable unsaturated bond, and may have a substituent such as a methyl group or an ethyl group. Vinyl group Examples of the unsaturated group R ^a, an allyl group, a methacryloxy group, an aminopropyl group, a glycidoxy group, and an alkenyl group and propargyl group. R ^b may be the same organic group as R ^a or a different organic group. Examples of the alkoxyl group R ^b O include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an isopropoxy group, and an s-butoxy group.

  Specific examples of unsaturated alkoxysilane monomers include trimethoxyvinylsilane, triethoxyvinylsilane, allyltrimethoxysilane, allyltriethoxysilane, tributoxyvinylsilane, tripropoxyvinylsilane, allyltributoxysilane, allyltripropoxysilane, dimethoxydivinylsilane, diallyl Dimethoxysilane, diethoxydivinylsilane, diallyldiethoxysilane, trimethoxy (3-butenyl) silane, triethoxy (3-butenyl) silane, di (3-butenyl) dimethoxysilane and di (3-butenyl) diethoxysilane .

An oligomer of unsaturated alkoxysilane may be used as a raw material for forming a silica skeleton. The unsaturated alkoxysilane oligomer also has at least one unsaturated group and an alkoxyl group. The unsaturated alkoxysilane oligomer is represented by the following general formula (2)
Si _m O _m-1 R ^a _{2m + 2-x} OR ^b _x (2)
(However, R ^a has an unsaturated bond and represents an organic group having 2 to 10 carbon atoms, R ^b O represents an alkoxyl group having 1 to 4 carbon atoms, m represents an integer of 2 to 5, x Represents an integer of 4 to 7.) is preferred. Preferred examples of the unsaturated group R ^a and the alkoxyl group R ^b O are the same as those of the above alkoxysilane monomer.

  The condensation number m is preferably 2 or 3. An oligomer having a condensation number m of 5 or less can be easily obtained by polymerization of a monomer using an acid catalyst, as will be described later. The number x of alkoxyl groups is preferably 3-5. If it is less than 3, hydrolytic polycondensation of alkoxysilane does not occur sufficiently, so that three-dimensional crosslinking is difficult and it is difficult to form a wet gel. When the number x of alkoxyl groups is more than 5, the ratio of unsaturated groups is too small, and the mechanical strength is not improved sufficiently by the polymerization reaction. Specific examples of the alkoxysilane oligomer having an unsaturated group include disilane, trisilane, and tetrasilane obtained by condensation of the above unsaturated group alkoxysilane monomer.

(b) Solvent The solvent is preferably composed of water and alcohol. As the alcohol, methanol, ethanol, n-propyl alcohol, and isopropyl alcohol are preferable, and ethanol is particularly preferable. The degree of activity of the hydrolysis polycondensation reaction depends on the molar ratio of water to the alkoxysilane or silsesquioxane monomer and / or oligomer (silica skeleton-forming compound). Accordingly, the molar ratio of water / alcohol does not directly affect the progress of the hydrolysis polycondensation reaction, but is preferably substantially 0.1 to 2. If the water / alcohol molar ratio is more than 2, the hydrolysis reaction proceeds too quickly. When the water / alcohol molar ratio is less than 0.1, the silica skeleton-forming compound is hardly hydrolyzed.

(c) Catalyst A catalyst for hydrolysis reaction is added to an aqueous solution of the silica skeleton-forming compound. The catalyst may be acidic or basic. For example, when an oligomer is obtained by condensing a silica skeleton-forming compound monomer in an aqueous solution containing an acidic catalyst and polymerized in a solution containing a basic catalyst, the hydrolysis reaction can proceed efficiently. . Examples of acidic catalysts include hydrochloric acid, nitric acid and acetic acid. Examples of basic catalysts include ammonia, amines, NaOH and KOH. Examples of preferred amines include alcohol amines and alkyl amines (for example, methylamine, dimethylamine, trimethylamine, n-butylamine, n-propylamine).

(d) Compounding ratio It is preferable to dissolve the silica skeleton-forming compound in a solvent so that the solvent / alkoxysilane molar ratio is 3 to 100. When the molar ratio is less than 3, the degree of polymerization of the alkoxysilane becomes too high, and when the molar ratio exceeds 100, the degree of polymerization of the alkoxysilane becomes too low. The catalyst / alkoxysilane molar ratio is preferably 1 × 10 ⁻⁷ to 1 × 10 ⁻¹ , more preferably 1 × 10 ⁻² to 1 × 10 ⁻¹ . If the molar ratio is less than 1 × 10 ⁻⁷ , the alkoxysilane hydrolysis reaction does not occur sufficiently. Even if the molar ratio exceeds 1 × 10 ⁻¹ , the catalytic effect does not increase. The molar ratio of water / alkoxysilane is preferably 0.5-20, and more preferably 5-10.

(e) Aging The solution containing the silica skeleton-forming compound condensed by hydrolysis is aged by standing at 25 to 90 ° C. or slowly stirring for about 20 to 60 hours. Gelation proceeds by aging, and a wet gel containing silicon oxide is generated.

(3-i-2) Dispersion of the dispersion medium The dispersion medium of the wet gel has a surface tension that promotes or delays aging and / or a contact angle between the solid-liquid phase and the range of surface modification in the organic modification process. In addition to the influence, it also relates to the evaporation rate of the dispersion medium in the coating process described later. The dispersion medium incorporated in the gel can be replaced with another dispersion medium by repeating the operation of pouring another dispersion medium, shaking and then decanting. Although the dispersion medium may be replaced before or after the organic modification reaction, it is preferably performed before the organic modification reaction from the viewpoint of reducing the number of steps.

  Examples of the substituted dispersion medium include ethanol, methanol, propanol, butanol, hexane, heptane, pentane, cyclohexane, toluene, acetonitrile, acetone, dioxane, methyl isobutyl ketone, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, and ethyl acetate. These dispersion media may be used alone or in combination.

  A preferred substituted dispersion medium is a ketone solvent. If the solvent is replaced with a ketone solvent by the ultrasonic treatment step described later, a highly dispersible organic-modified silica-containing sol can be obtained. Since the ketone solvent has an excellent affinity for silica (silicon oxide) and organically modified silica, the organically modified silica is well dispersed in the ketone solvent. A preferred ketone solvent has a boiling point of 60 ° C. or higher. Ketones having a boiling point of less than 60 ° C. are too volatile in the ultrasonic irradiation process described below. For example, when acetone is used as a dispersion medium, a large amount of acetone is volatilized during ultrasonic irradiation, so that it is difficult to adjust the concentration of the dispersion. In addition, there is also a problem that sufficient film formation time cannot be obtained because the film is volatilized too quickly in the film formation process. Furthermore, acetone is known to be harmful to the human body and is not preferable from the viewpoint of worker health.

  Particularly preferred ketone solvents are asymmetric ketones having different substituents on both sides of the carbonyl group. Since the asymmetric ketone has a large polarity, it has a particularly excellent affinity for silica and organically modified silica. In the dispersion, the organically modified silica preferably has a particle size of 200 nm or less. When the particle diameter of the organically modified silica is larger than 200 nm, it is difficult to form a silica airgel film having a substantially smooth surface.

  The substituent that the ketone has may be an alkyl group or an aryl group. Preferred alkyl groups are those having about 1 to 5 carbon atoms. Specific examples of the ketone solvent include methyl isobutyl ketone, ethyl isobutyl ketone, and methyl ethyl ketone.

(3-i-3) Organic Modification By adding an organic modifier solution to the wet gel, a hydrophilic group such as a hydroxyl group at the terminal of silicon oxide constituting the wet gel is replaced with a hydrophobic organic group.
(a) Organic modifier
(a-1) Saturated organic modifier A preferred saturated organic modifier is represented by the following formulas (3) to (8):
R ^c _p SiCl _q・ ・ ・ (3)
R ^c ₃ SiNHSiR ^c ₃ ... (4)
R ^c _p Si (OH) _q・ ・ ・ (5)
R ^c ₃ SiOSiR ^c ₃ ... (6)
R ^c _p Si (OR ^b ) _q・ ・ ・ (7)
R ^c _p Si (OCOCH ₃ ) _q・ ・ ・ (8)
(Wherein p represents an integer of 1 to 3, q represents an integer of 1 to 3 satisfying the condition of q = 4-p, R ^b O represents an alkoxyl group having 1 to 4 carbon atoms, and R ^c represents hydrogen. A substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, or a substituted or unsubstituted aryl group having 5 to 18 carbon atoms), or a mixture thereof.

  Specific examples of saturated organic modifiers include triethylchlorosilane, trimethylchlorosilane, diethyldichlorosilane, dimethyldichlorosilane, acetoxytrimethylsilane, acetoxysilane, diacetoxydimethylsilane, methyltriacetoxysilane, phenyltriacetoxysilane, diphenyldiacetoxysilane, Trimethylethoxysilane, trimethylmethoxysilane, 2-trimethylsiloxypent-2-en-4-one, n- (trimethylsilyl) acetamide, 2- (trimethylsilyl) acetic acid, n- (trimethylsilyl) imidazole, trimethylsilylpropiolate, nonamethyl Trisilazane, hexamethyldisilazane, hexamethyldisiloxane, trimethylsilanol, triethylsilanol, triphenylsilanol, t-butyldimethyl Examples include silanol and diphenylsilanediol.

(a-2) Unsaturated organic modifier When an unsaturated organic modifier is used, a silica airgel film having excellent toughness can be obtained even when the amount of the binder is small. Preferred examples of the unsaturated organic modifier include the following formulas (9) to (14):
R ^d _p SiCl _q ... (9)
R ^d ₃ SiNHSiR ^d ₃ ... (10)
R ^d _p Si (OH) _q・ ・ ・ (11)
R ^d ₃ SiOSiR ^d ₃ ... (12)
R ^d _p Si (OR ^d ) _q・ ・ ・ (13)
R ^d _p Si (OCOCH ₃ ) _q・ ・ ・ (14)
(However, p is an integer of 1 to 3, q represents an integer of 1 to 3 that satisfies the condition of q = 4-p, R ^d has an ultraviolet-polymerizable unsaturated bond, and has 2 to 10 carbon atoms. Represents an organic group. The unsaturated group R ^d may have a substituent such as a methyl group or an ethyl group. Vinyl group Examples of the unsaturated group R ^d, allyl group, methacryloxy group, an aminopropyl group, a glycidoxy group, and an alkenyl group and propargyl group. The unsaturated organic modifier may be one type or two or more types. A saturated organic modifier may be used in combination with the unsaturated organic modifier.

  The unsaturated organic modifier is preferably an unsaturated chlorosilane, more preferably an unsaturated monochlorosilane having three unsaturated groups. Specific examples of unsaturated organic modifiers include triallylchlorosilane, diallyldichlorosilane, triacetoxyallylsilane, diacetoxydiallylsilane, trichlorovinylsilane, dichlorodivinylsilane, triacetoxyvinylsilane, diacetoxydiallylsilane, trimethoxy (3-butenyl) silane , Triethoxy (3-butenyl) silane, di (3-butenyl) dimethoxysilane, di (3-butenyl) diethoxysilane, and the like.

(b) Organic modification reaction The organic modifier is preferably dissolved in a solvent such as hydrocarbons such as hexane, cyclohexane, pentane and heptane, ketones such as acetone, and aromatic compounds such as benzene and toluene. Although depending on the type and concentration of the organic modifier, the organic modification reaction is preferably allowed to proceed at 10 to 40 ° C. When it is less than 10 ° C., the organic modifier does not easily react with silicon oxide. If it exceeds 40 ° C., the organic modifier reacts easily with substances other than silicon oxide. During the reaction, it is preferable to stir the solution so that there is no distribution in the temperature and concentration of the solution. For example, when the organic modifier solution is a hexane solution of triethylchlorosilane, the silanol group is sufficiently silylated when held at 10 to 40 ° C. for about 20 to 40 hours (for example, 30 hours).

(3-i-4) Ultrasonic Treatment By ultrasonic treatment, the gel-like and / or sol-form organic modified silica can be brought into a state suitable for coating. In the case of gel-like organically modified silica, it is considered that the gel aggregated by electrical force or van der Waals force is dissociated by ultrasonic treatment or the covalent bond between silicon and oxygen is broken, resulting in a dispersed state. It is done. Even in the case of a sol, aggregation of colloidal particles can be reduced by ultrasonic treatment. For the ultrasonic treatment, a dispersion device using an ultrasonic transducer can be used. The frequency of the ultrasonic wave to be irradiated is preferably 10 to 30 kHz. The output is preferably 300 to 900 W.

  The ultrasonic treatment time is preferably 5 to 120 minutes. The longer the ultrasonic wave is irradiated, the finer the gel and / or sol clusters become, and the less aggregated the state becomes. For this reason, colloidal particles of organically modified silica are in a state close to monodispersion in a silica-containing sol obtained by ultrasonic treatment. When it is less than 5 minutes, the colloidal particles are not sufficiently dissociated. Even when the sonication time is longer than 120 minutes, the dissociation state of the organically modified silica colloidal particles hardly changes.

  In order to form a silica airgel film having a porosity of 20-60% and a refractive index of 1.25-1.30, the ultrasonic frequency is 10-30 kHz, the output is 300-900 W, and ultrasonic treatment is performed. The time is preferably 5 to 120 minutes.

  A dispersion medium may be added so that the concentration and fluidity of the wet gel are in an appropriate range. A dispersion medium may be added prior to ultrasonic treatment, or a dispersion medium may be added after ultrasonic treatment to some extent. The mass ratio of the organically modified silica to the dispersion medium is preferably 0.1 to 20%. If the mass ratio of the organically modified silica to the dispersion medium is not in the range of 0.1 to 20%, it is difficult to form a uniform thin layer, which is not preferable.

  When a sol containing silicon oxide colloidal particles in a state close to monodispersion is used, an organic modified silica airgel film having a small porosity can be formed. When a sol containing colloidal particles in a large aggregated state is used, a silica airgel film having a large porosity can be formed. Therefore, the ultrasonic treatment time affects the porosity of the silica airgel film. By applying a sol that has been subjected to ultrasonic treatment for 5 to 120 minutes, an organically modified silica airgel film having a porosity of 20 to 60% can be obtained.

(3-ii) Preparation of UV-curable resin solution The UV-curable resin that acts as a binder for organically modified silica is preferably compatible with the dispersion of organically modified silica. The solvent is not particularly limited as long as it can dissolve the ultraviolet curable resin and is compatible with the organic modified silica dispersion. Therefore, what is necessary is just to select suitably from what was described above as a substituted dispersion medium of an organic modification silica dispersion liquid.

  The ultraviolet curable resin preferably has a refractive index of 1.5 or less after curing, and more preferably has a refractive index of 1.3 to 1.4. When an ultraviolet curable resin having a refractive index of 1.5 or less after curing is used, the refractive index of the silica airgel film can be set to 1.2 to 1.3. Fluorine-based non-crystalline ultraviolet curable resin is preferable because it has a refractive index of 1.5 or less and excellent transparency. Specific examples of the non-crystalline ultraviolet curable fluorine resin include a fluoroolefin copolymer, a polymer having a fluorine-containing aliphatic ring structure, and a fluorinated acrylate copolymer.

  An example of a fluoroolefin copolymer is a copolymer of 37 to 48% by mass of tetrafluoroethylene, 15 to 35% by mass of vinylidene fluoride, and 26 to 44% by mass of hexafluoropropylene. .

  Examples of the polymer having a fluorinated alicyclic structure include those obtained by polymerizing a monomer having a fluorinated alicyclic structure, and those obtained by cyclopolymerizing a fluorinated monomer having at least two polymerizable double bonds. A polymer obtained by polymerization of a monomer having a fluorine-containing ring structure is described in JP-B-63-18964. This polymer can be obtained by homopolymerization of a monomer having a fluorine-containing ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole) or copolymerization with a radical polymerizable monomer such as tetrafluoroethylene.

  Polymers obtained by cyclopolymerization of fluorine-containing monomers having at least two polymerizable double bonds are described in JP-A Nos. 63-238111 and 63-238115. This polymer is obtained by cyclopolymerization of monomers such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether), or copolymerization with a radical polymerizable monomer such as tetrafluoroethylene. Examples of the copolymer include a monomer having a fluorine-containing ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole) and at least two such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether). Examples thereof include those obtained by copolymerizing fluorine-containing monomers having two polymerizable double bonds.

  The binder may be made of a resin other than a fluorine-based resin, or a fluorine-based resin and another resin. Examples of resins other than fluorine-based resins include acrylic resins, silicone resins, epoxy resins, and urethane resins.

(3-iii) Preparation of coating liquid The coating liquid contains organically modified silica, one or more ultraviolet curable resins, and a photopolymerization initiator. The coating solution is either (a) a dispersion containing organically modified silica and a solution containing an ultraviolet curable resin and a polymerization initiator, or (b) a dispersion containing organically modified silica and a polymerization initiator. Liquid and a solution containing an ultraviolet curable resin, or (c) a dispersion containing organically modified silica and a photopolymerization initiator, and a solution containing an ultraviolet curable resin and a photopolymerization initiator. It can be prepared by mixing or (d) adding a photopolymerization initiator after mixing a dispersion containing organically modified silica and a solution containing an ultraviolet curable resin. As described above, the content of the organically modified silica in the dispersion before mixing is preferably 0.1 to 20% by mass with respect to the dispersion medium. When the fluoroolefin copolymer is used as a binder, the concentration of the copolymer is preferably 0.5 to 2.0% by mass.

  The organic modified silica-containing dispersion and the ultraviolet curable resin solution are preferably mixed so that the volume ratio of the organic modified silica to the ultraviolet curable resin in the coating solution is 9: 1 to 1: 9. If the volume ratio of the ultraviolet curable resin in the coating solution exceeds 90%, the silica airgel voids are filled with the resin and the refractive index of the silica airgel film becomes too high. When the volume ratio of the ultraviolet curable resin is less than 10%, the ratio of the binder is too small, and the toughness of the silica airgel film is too small.

  The photopolymerization initiator is added to such an extent that the ultraviolet curable resin, or the unsaturated group of the ultraviolet curable resin and the organically modified silica can be polymerized in the ultraviolet irradiation step described later. A photopolymerization initiator may be added in advance to the ultraviolet curable resin solution and / or the organic modified silica-containing dispersion, or may be added after mixing both. The photopolymerization initiator is preferably 1 to 15% by mass in terms of solid content in the coating solution.

  Specific examples of photopolymerization initiators include benzoin and derivatives thereof (benzoin methyl ether, benzoin isopropyl ether, benzoin isobutyl ether, etc.), benzyl derivatives (benzyl dimethyl ketal, etc.), alkylphenones (acetophenone, 2,2-dimethoxy-2) -Phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropane-1 -One), anthraquinone and its derivatives (2-methylanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, etc.), thioxanthone and its derivatives (2,4-dimethylthioxanthone, 2-chlorothioxanthone) Etc.), Benzophenone And derivatives thereof (N, N-dimethylaminobenzophenone and the like).

(4) Forming method of the first layer The first layer 11 of the antireflection film is preferably formed by a physical film forming method. Examples of the physical film forming method include a vacuum deposition method and a sputtering method. Of these, the vacuum deposition method is particularly preferable in terms of manufacturing cost and processing accuracy.

  Examples of the vacuum evaporation method include a resistance overheating method and an electron beam method, but the electron beam method vacuum evaporation method will be described below. A vacuum deposition apparatus 30 shown in FIG. 8 is a deposition source in which a rotatable rotating rack 32 for placing a plurality of lenses on the inner surface and a crucible 36 for placing a deposition material are provided in a vacuum chamber 31. 33, an electron beam irradiator 38, a heater 39, and a vacuum pump connection port 35 connected to the vacuum pump 40. In order to form the first layer of the antireflection film on the lens 100, first, the lens 100 is placed on the rotating rack 32 so that the surface faces the vapor deposition source 33, and the vapor deposition material 37 is placed on the crucible 36. Subsequently, the inside of the vacuum chamber 31 is depressurized by the vacuum pump 40 connected to the vacuum pump connection port 35, and then the lens 100 is heated by the heater 39, and the rotating rack 32 is rotated by the rotating shaft 34 while the deposition material 37 is applied. The deposition material 37 is heated by irradiating an electron beam from the electron beam irradiator 38. The vapor deposition material 37 evaporated by heating is vapor-deposited on the surface of the lens 100, and an antireflection film layer is formed on the surface of the lens 100.

In the vacuum deposition method, the initial degree of vacuum is preferably, for example, 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻⁶ Torr. If the degree of vacuum is outside this range, the vapor deposition takes time and the production efficiency is deteriorated, or the vapor deposition is often insufficient and the film formation may not be completed. In order to increase the accuracy of the formed film, it is preferable to heat the lens during vapor deposition. The temperature of the lens during vapor deposition can be appropriately determined according to the heat resistance of the lens and the vapor deposition rate, but is preferably 60 to 250 ° C, for example.

(5) Method of forming the second layer
(5-i) Coating The second layer 12 is formed by a wet method. When the coating liquid is applied to a substrate or the like, the dispersion medium is volatilized and a film made of organically modified silica, an ultraviolet curable resin, and a photopolymerization initiator is formed. Examples of coating methods include spray coating, spin coating, dip coating, flow coating, and bar coating. A preferred coating method is a spin coating method. According to the spin coating method, a layer having a uniform thickness can be formed.

(5-ii) Drying The solvent in the coating solution is volatile and may be naturally dried. However, drying at a temperature of 50 to 100 ° C. can be accelerated. The porosity of the organically modified silica decreases due to gel shrinkage caused by capillary pressure while the dispersion medium is volatilized, but recovers by the springback phenomenon when volatilization is completed. For this reason, the porosity of the organic modified silica airgel film obtained by drying is almost the same as the original porosity of the gel network, and shows a large value. The shrinkage and springback phenomenon of the silica gel network is described in detail in US Pat. No. 5,948,482.

(5-iii) UV irradiation The coating film is irradiated with UV to polymerize the UV curable resin, or the unsaturated group of the UV curable resin and the organically modified silica. It is preferable to irradiate the coating film with ultraviolet rays of about 50 to 10,000 mJ / cm ² using an ultraviolet irradiation device. Although depending on the thickness of the coating film, in the case of about 10 to 2000 nm, the irradiation time is preferably about 1 to 30 seconds.

(5-iv) Firing The coated film is preferably fired at 50 to 150 ° C. By baking, the solvent in the layer, the hydroxyl groups on the surface, and the like can be removed to increase the strength of the film. Also, if the firing temperature is about 50 to 150 ° C., decomposition hardly occurs, so the silica airgel film after firing is cured by polymerization of unsaturated groups of ultraviolet curable resin or ultraviolet curable resin and organically modified silica. Has resin.

  As described above, excellent low reflectance characteristics can be obtained by forming the antireflection film 1 having the above configuration on the substrate 3. Specifically, the reflectance in the wavelength region 450 nm to 600 nm of 0 ° incident light of the antireflection film 1 is preferably 0.5% or less, and more preferably 0.45% or less. The reflectance of 30 ° incident light in the wavelength region of 400 nm to 650 nm is preferably 1.0% or less, and more preferably 0.95% or less.

[2] Substrate The substrate 3 has a refractive index of light in the wavelength region of 400 to 700 nm of 1.70 to 1.95,
It is preferably 1.75 to 1.94. When the refractive index of the substrate 3 is in such a range, the optical performance can be satisfactorily improved in the visible light wavelength band, and the interchangeable lens can be made compact.

  As the material of the substrate 3, for example, optical glass such as LaSFN9, LaSF01, LaSF016, SF03, SFS01 is particularly preferable.

[3] Fluororesin-based film In the present invention, as shown in FIG. Unless otherwise specified, a fluororesin film 23 having “water / oil repellency” may be provided.

  The material of the fluororesin film 23 is not particularly limited as long as it is colorless and highly transparent, and general materials can be used. Examples of the material of the fluororesin film include an organic compound containing fluorine and an organic-inorganic hybrid polymer containing fluorine.

  Examples of the fluorine-containing organic compound include a fluororesin and a fluorinated pitch [for example, CFn (n: 1.1 to 1.6)]. Examples of the fluororesin include a polymer of a fluorine-containing olefin compound, and a copolymer comprising a fluorine-containing olefin compound and a monomer copolymerizable therewith. Examples of such (co) polymers include polytetrafluoroethylene (PTFE), tetraethylene-hexafluoropropylene copolymer (PFEP), ethylene-tetrafluoroethylene copolymer (PETFE), tetrafluoroethylene-par. Fluoroalkyl vinyl ether copolymer (PFA), ethylene-chlorotrifluoroethylene copolymer (PECTFE), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (PEPE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF). A polymer obtained by polymerizing a commercially available fluorine-containing composition may be used as the fluororesin. Examples of commercially available fluorine-containing compositions include Opstar (manufactured by JSR Corporation) and Cytop (manufactured by Asahi Glass Co., Ltd.).

Examples of the organic-inorganic hybrid polymer containing fluorine include an organosilicon polymer having a fluorocarbon group. Examples of the organosilicon polymer having a fluorocarbon group include a polymer obtained by hydrolyzing a fluorine-containing silane compound having a fluorocarbon group. As the fluorine-containing silane compound, the following formula (15):
CF ₃ (CF ₂ ) _a (CH ₂ ) ₂ SiR _b X _c ... (15)
(However, R is an alkyl group, X is an alkoxy group or a halogen atom, a is an integer of 0-7, b is an integer of 0-2, c is an integer of 1-3, b + c = 3)). Specific examples of the compound represented by the formula (15) include CF ₃ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CH ₂ ) ₂ SiCl ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ SiCl ₃ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ SiCl ₃ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₃ SiCH ₃ (OCH ₃ ) ₂ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ SiCH ₃ Cl _{2 and the} like. Examples of commercially available organosilicon polymers include Novec EGC-1720 (Sumitomo 3M), XC98-B2472 (GE Toshiba Silicone) and X71-130 (Shin-Etsu Chemical Co., Ltd.).

  The thickness of the fluororesin film 23 is preferably 0.4 to 100 nm, and more preferably 10 to 80 nm. When the thickness of the fluororesin film is less than 0.4 nm, the water / oil repellency is insufficient. On the other hand, if it exceeds 100 nm, transparency is impaired and the optical characteristics of the antireflection film are changed. The refractive index of the fluororesin-based film is preferably 1.5 or less, and more preferably 1.45 or less. The fluororesin film may be formed by a vacuum deposition method, but is preferably formed by a wet method such as a sol-gel method.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
The antireflection film 1 of Example 1 was formed according to the layer structure shown in Table 1. The refractive index of each layer is the refractive index for light having a wavelength of 550 nm. The formation procedure of each layer is shown below.

[1] Formation of the first layer
An antireflection film of the first layer shown in Table 1 was formed on the surface of the optical lens made of SFS01 by an electron beam vacuum deposition method using the apparatus shown in FIG. Here, the conditions for vapor deposition were an initial vacuum of 1.2 × 10 ⁻⁵ Torr and a substrate temperature of 230 ° C.

[2] Formation of the second layer The silica airgel layer of the second layer was formed by a sol-gel method.

(2-i) Preparation of silica wet gel After mixing 5.21 g of tetraethoxysilane and 4.38 g of ethanol, 0.4 g of hydrochloric acid (0.01 N) was added and stirred for 90 minutes, and then 44.3 g of ethanol and aqueous ammonia solution ( 0.02 N) 0.5 g was added and stirred for 46 hours. When the resulting mixture was heated to 60 ° C. and aged for 46 hours, a silica wet gel was formed.

(2-ii) Preparation of organically modified silica dispersion Add ethanol to silica wet gel, shake for 10 hours, and then decantate to remove unreacted materials and replace the dispersion medium of wet gel with ethanol did. Subsequently, methyl isobutyl ketone (MIBK) was added to the ethanol-dispersed wet gel, shaken for 10 hours, and decanted to replace the dispersion medium from ethanol to MIBK.

  A trimethylchlorosilane solution (concentration: 5% by volume) containing MIBK as a solvent was added to a silica wet gel, and stirred for 30 hours to organically modify the silicon oxide terminal. MIBK was added to the obtained organic modified silica wet gel, and the mixture was shaken for 24 hours and washed by decantation.

After adding MIBK to organic modified silica wet gel to a concentration of 3% by mass,
Sol-form organic modified silica (organic modified silica dispersion) was produced by ultrasonic irradiation (20 kHz, 500 W) for 20 minutes.

(2-iii) Preparation of coating solution The organically modified silica dispersion obtained in step (2-ii) and the low refractive index UV curable resin solution [trade name “AR100” manufactured by Daikin Industries, Ltd.] The mixture was mixed at a volume ratio of 1 to obtain an organically modified silica-containing coating solution.

(2-iv) Spin coating The organic-modified silica-containing coating solution obtained in the step (2-iii) is applied onto the first layer by a spin coating method, and using a UV irradiation device (manufactured by Fusion Systems). After polymerizing by irradiating with ultraviolet rays at 1500 mJ / cm ² and baking for 1 hour at 150 ° C., a hydrolysis polycondensation reaction occurs, and a silica airgel layer having an organic modified chain with a predetermined film thickness shown in Table 1 is formed. Been formed.

Example 2
In the same manner as in Example 1, the antireflection film of Example 2 was formed according to the layer structure shown in Table 2.

Example 3
In the same manner as in Example 1, the antireflection film of Example 3 was formed according to the layer structure shown in Table 3.

Example 4
In the same manner as in Example 1, the antireflection film of Example 4 was formed according to the layer structure shown in Table 4. The second layer of silica airgel was formed using SiosoITM [manufactured by Merck Co., Ltd.] as a material, under conditions of a firing temperature of 550 ° C. and a firing time of 5 minutes.

Example 5
In the same manner as in Example 1, an antireflection film composed of the first layer and the second layer shown in Table 5 was formed on the optical lens composed of SFS01. Further, a fluororesin film was formed on the second layer by the following method.

3 g of a silicone-based fluororesin [manufactured by Shin-Etsu Chemical Co., Ltd., trade name “X71-130”] was added to 60 g of hydrofluoroether to prepare a fluororesin-based liquid. The optical lens on which the first layer and the second layer were formed was immersed in a fluororesin-based liquid, applied by pulling up at 300 mm / min, and dried at room temperature for 24 hours to form a fluororesin-based film.

Comparative Example An antireflection film of a comparative example was formed in accordance with the layer structure shown in Table 6. The first to eighth layers were formed in the same procedure as the first layer of Example 1.

  FIG. 3 shows the spectral characteristics of reflectance when light having a wavelength region of 350 nm to 850 nm is applied to the optical lenses having antireflection films obtained in Examples 1 to 4 and the comparative example at incident angles of 0 ° and 30 °. To FIG. The medium in contact with the outermost layer was air. Each figure shows the reflectivity from 0% to 5%.

  As shown in FIGS. 3 to 6 in Examples 1 to 4, it has an excellent low reflectance characteristic in a visible light region of a wavelength region of 400 nm to 700 nm in both cases of an incident angle of 0 ° and 30 °. I understood it.

  On the other hand, in the comparative example, as shown in FIG. 7, when the incident angle was 0 °, the reflectance near a wavelength of 450 nm was higher than 0.5%.

  Further, no flare or ghost occurred in the images taken using the optical lenses obtained in Examples 1 to 5.

  On the other hand, flare and ghost were seen in the image taken using the optical lens obtained by the comparative example.

It is sectional drawing which shows the anti-reflective film by one Example of this invention formed in the surface of a board | substrate. It is sectional drawing which shows the antireflection film by another Example of this invention formed in the surface of a board | substrate. It is a graph showing the spectral reflectance of the anti-reflective film by Example 1 of this invention. It is a graph showing the spectral reflectance of the anti-reflective film by Example 2 of this invention. It is a graph showing the spectral reflectance of the anti-reflective film by Example 3 of this invention. It is a graph showing the spectral reflectance of the anti-reflective film by Example 4 of this invention. It is a graph showing the spectral reflectance of the antireflection film of a comparative example. It is a block diagram which shows an example of the apparatus which forms an antireflection film.

Explanation of symbols

1, 2 ... Antireflection film 3 ... Substrate

Claims (8)

An antireflection film in which a first layer and a second layer are laminated in this order from the substrate side on a substrate, and in the light of a wavelength region of 400 to 700 nm,
The refractive index of the substrate is 1.70 to 1.95,
The first layer is mainly composed of alumina, the optical film thickness is 98.5 to 133.5 nm, the refractive index is 1.59 to 1.68,
The second layer is a silica airgel layer, an optical film thickness of Ri 116.0 to 129.0 nm der antireflection film having a refractive index, characterized in that a 1.22 to 1.28. 2. The antireflection film according to claim 1 , wherein a reflectance of 0 ° incident light in a wavelength region of 450 nm to 600 nm is 0.5% or less, and a reflectance of 30 ° incident light in a wavelength region of 400 nm to 650 nm is 1.0. % Anti-reflective coating, characterized by 3. The antireflection film according to claim 1 , further comprising a fluororesin-based film having a thickness of 0.4 nm to 100 nm having water repellency or water / oil repellency on the second layer. Prevention film. The antireflection film according to any one of claims 1 to 3 , wherein the first layer is formed by a physical film formation method, and the second layer is formed by a wet method. The anti-reflection coating according to any one of claims 1-4, wherein the physical deposition method is a vacuum deposition method, the wet method is a sol - antireflection film, which is a gel method. Optical component characterized by having an antireflection film according to any one of claims 1-5. An interchangeable lens comprising the optical component according to claim 6 . An imaging apparatus comprising the optical component according to claim 6 .

Images